Microscopic DTI accurately identifies early glioma cell migration: correlation with multimodal imaging in a new glioma stem cell model

Abstract

Monitoring glioma cell infiltration in the brain is critical for diagnosis and therapy. Using a new glioma Glio6 mouse model derived from human stem cells we show how diffusion tensor imaging (DTI) may predict glioma cell migration/invasion. In vivo multiparametric MRI was performed at one, two and three months of Glio6 glioma growth (Glio6 (n = 6), sham (n = 3)). This longitudinal study reveals the existence of a time window to study glioma cell/migration/invasion selectively. Indeed, at two months only Glio6 cell invasion was detected, while tumor mass formation, edema, blood-brain barrier leakage and tumor angiogenesis were detected later, at three months. To robustly confirm the potential of DTI for detecting glioma cell migration/invasion, a microscopic 3D-DTI (80 μm isotropic spatial resolution) technique was developed and applied to fixed mouse brains (Glio6 (n = 6), sham (n = 3)). DTI changes were predominant in the corpus callosum (CC), a known path of cell migration. Fractional anisotropy (FA) and perpendicular diffusivity (D ) changes derived from ex vivo microscopic 3D-DTI were significant at two months of tumor growth. In the caudate putamen an FA increase of +38% (p < 0.001) was observed, while in the CC a - 28% decrease in FA (p < 0.005) and a + 95% increase in D (p < 0.005) were observed. In the CC, DTI changes and fluorescent Glio6 cell density obtained by two-photon microscopy in the same brains were correlated (p < 0.001, r = 0.69), validating FA and D as early quantitative biomarkers to detect glioma cell migration/invasion. The origin of DTI changes was assessed by electron microscopy of the same tract, showing axon bundle disorganization. During the first two months, Glio6 cells display a migratory phenotype without being associated with the constitution of a brain tumor mass. This offers a unique opportunity to apply microscopic 3D-DTI and to validate DTI parameters FA and D as biomarkers for glioma cell invasion.

Diffusion tensor imaging and arterial tissue: establishing the influence of arterial tissue microstructure on fractional anisotropy, mean diffusivity and tractography

“…This becomes even more evident in the tractography results -where the decellularised vessels yield no helically arranged tracts ( Figure 5). This result highlights the significance of cellular content and corroborates findings in a previous ex vivo DTI study on cell migration in brain tumours 40 , where the authors saw a decrease in FA and increase in MD when cells migrated out of a region of interest.…”

3D imaging of the brain morphology and connectivity defects in a model of psychiatric disorders: MAP6-KO mice

“…In mouse models, the very small brain volume is a real limitation to achieving high spatial resolution in a reasonable time-frame as the signal-to-noise ratio achievable for a single image voxel tends to be low. For the purposes of this study, DTI was performed ex vivo using exogenous gadolinium-based MRI contrast agents 30 , 31 to reduce the relaxation times, in particular the longitudinal value T 1 . In these conditions, acquisition time was accelerated, and a high isotropic spatial resolution (80 µm) was attained with a signal-to-noise ratio of 104.…”

“…After removing surrounding skin and muscles, the skulls containing intact brains were immersed in the fixing solution for four days, and then transferred to a Fomblin (FenS chemicals) bath for at least eleven days after brain fixation. This schedule provided homogeneous distribution of the Gd-DOTA throughout the whole brain 31 .…”

Motor cortex gliomas induces microstructural changes of large fiber tracts revealed by TBSS

“…Owing to the specific anatomical location of the frontal lobe, the relationship between motor cortex gliomas and the surrounding fiber bundles is more complicated than for other intracranial tumors. Previous investigations 13 – 15 focused on the qualitative analysis of fiber bundles that may be involved in motor cortex tumors using traditional imaging data. These studies were only able to assess changes in the surrounding fibers due to invasion or edema.…”

“…A DTI glioma study revealed significant glioma-related changes in many white matter regions, including changes in the degree of anisotropy, average diffusion coefficient (AD), and other DTI coefficients; however, no conventional MRI study has reported glioma-related signal changes 11,12 . These changes identified by DTI may indicate the invasion and spread of early tumor cell precursors that may not be detected with conventional MRI 13 . However, previous studies have typically focused on the analysis of FA dispersion values and related issues of one or more white matter fiber pathways, but overall have lacked voxel-level assessments.…”